1. Field of the Invention
The invention relates to a rolling bearing.
2. Description of the Related Art
A rolling bearing is used to support a shaft of a rotating portion included in a vehicle or a machine tool. A rolling bearing depicted in FIG. 12 is a tapered roller bearing 90. The tapered roller bearing 90 includes an inner ring 91, an outer ring 92, a plurality of tapered rollers 93, and an annular cage 94 (see, for example, Japanese Patent Application Publication No. 2005-69421 (JP 2005-69421 A). The tapered rollers 93 are provided between the inner ring 91 and the outer ring 92. The cage 94 holds the tapered rollers 93 at intervals in a circumferential direction.
Such a tapered roller bearing 90 is used, for example, for a transmission in an automobile, in order to support a shaft that rotates along with a gear. In this case, a lubricant stored in a housing of the transmission and used to lubricate the gear is also used to lubricate the tapered roller bearing 90.
In the tapered roller bearing 90 depicted in FIG. 12, a pump action resulting from rotation of the tapered roller bearing 90 causes the lubricant stored in the housing and that is present in a bearing exterior to flow from between a small-diameter-side end portion 95 of the cage 94 and an inner-ring outer periphery 96 and from between the small-diameter-side end portion 95 of the cage 94 and an outer-ring inner periphery 97 into a bearing interior where the tapered rollers 93 are present. The lubricant having flowed into the bearing interior passes through the bearing interior.
In the transmission in the automobile, the lubricant contains foreign matter such as abrasive powder resulting from manufacture of a gear or the like or wear debris resulting from driving of the gear. Therefore, when such foreign matter passes through the bearing interior along with the lubricant, the foreign matter may be caught between the tapered rollers 93 and raceway surfaces 91a and 92a. Consequently, rolling contact surfaces of the tapered rollers 93 and the raceway surfaces 91a and 92a may suffer surface roughness, leading to a shortened life of the bearing.
The shortened life of the bearing caused by the foreign matter contained in the lubricant is not limited to the tapered roller bearing 90 as depicted in FIG. 12. Other rolling bearings such as ball bearings and cylindrical roller bearings may suffer such a reduction in life.